You've seen a water filter that costs a few hundred pesos and a system that costs several thousand, and both are described as “water filtration.” The obvious question is what could possibly justify the gap.

It's a fair question, and the answer isn't that the expensive one is simply better. They do different jobs. In a Mexico City apartment, which job you need depends on whether you're trying to improve the taste of your tap water or actually drink it.

What faucet and pitcher water filters actually do

A faucet mount or a pitcher filter (a Brita and its equivalents) is built around activated carbon. Carbon is genuinely good at what it does: it pulls out chlorine, reduces odor, and improves taste noticeably. Paired with a sediment layer, it also catches rust and the cloudiness that older Mexico City building pipes tend to add.

If your water tastes like a swimming pool, a carbon filter fixes that, and it fixes it for a fraction of the cost of anything else on our menu, or of the garrafones you'd otherwise keep carrying up the stairs. We sell them, and for the right person they're the right purchase.

What a carbon faucet filter can't remove

Carbon works by adsorption: contaminants stick to the surface of the carbon as water passes through. That's a chemical process, not a physical barrier, and it isn't a reliable defense against bacteria or parasitic cysts. The pores in a carbon block are far too large to stop them by size.

It can get worse than simply not helping. Research on point-of-use carbon block filters has found that as a cartridge approaches its rated volume, bacterial counts in the water leaving the filter can climb well above what went in: carbon removes the chlorine that was suppressing bacterial growth, and an aging cartridge becomes a surface bacteria can colonize. Replacing the cartridge on schedule brings that back down, which is exactly why the schedule exists.

So a faucet filter can make questionable water taste clean without making it safe to drink. That gap is the entire reason full systems exist, and it's the part the packaging rarely spells out.

What a full drinking water system does differently

An ultrafiltration or reverse osmosis system adds something a carbon water filter can't provide: a membrane with pores small enough to physically block pathogens.

Our ultrafiltration membranes are rated to 0.01 microns. Bacteria and parasitic cysts are larger than that, so they don't get through. It isn't adsorption doing the work; the pores are simply too small for them to physically fit. Reverse osmosis goes finer still, down to around 0.0001 microns, which also captures dissolved solids like heavy metals and fluoride.

That's the difference you're paying for. Not a better version of the same thing — a different mechanism that addresses a different risk.

What “removes 99% of contaminants” actually means

Plenty of water filter marketing says things like “removes 99% of contaminants” without ever naming which contaminants. That phrasing is doing a lot of work, and it's how people end up believing a carbon filter has made their water safe to drink.

We'd rather be specific. A faucet mount reduces chlorine, odor, and sediment. It is not rated to make water safe to drink straight from the tap, and we say so on the product page itself.

How to choose a water filter for a CDMX apartment

If your goal is better-tasting water for cooking, coffee, or rinsing produce (water you're going to boil anyway), a faucet mount does that job well and cheaply. Buying a full system for this is overspending.

If your goal is water you can drink straight from the tap, you need a membrane, and a carbon filter won't get you there no matter how good it tastes afterward. This is the usual answer in the older Roma Norte and Condesa buildings we work in, where the tap water is treated at the source but travels through decades-old plumbing and a rooftop tinaco to reach you.

Plenty of households end up with both: a drinking water system at the kitchen sink, and simpler filters elsewhere in the apartment where the water isn't being consumed.

Our Drinking Water Systems comparison covers the membrane options, and the Kitchen Faucet Mount page is upfront about what that tier is and isn't for.

Sources

  • Effect of Point-of-Use Activated Carbon Filters on the Bacterial Quality of Drinking Water — on heterotrophic plate counts rising in filter effluent as cartridges approach their rated volume, and falling again after replacement.
  • “The microbial colonization of activated carbon block point-of-use filters,” Environmental Science: Water Research & Technology, 2017.